The present invention relates generally to a pump construction and more particularly the internal passageways of the pump.
The pump industry now has available computational fluid dynamic based machine design software that allows pumps to be designed to achieve various performance parameters. The resultant designs require a high degree of dimensional precision to obtain the desired performance characteristics. The challenge is to convert the complex computer design into actual components.
To produce the desired geometry for internal casing components, investment castings are often used. Investment castings use metal molds that produce a wax pattern that in turn is used to make a ceramic mold. The wax pattern is then heated so that the wax melts and is removed which leaves the ceramic mold. The ceramic mold is then used to produce the metal parts for the pump. The ceramic mold produces high quality castings having a good surface finish and dimensional accuracy. However, investment casting tooling is expensive and is best suited to small size, mass produced parts. For custom designed pumps, the parameters of the pump need to match the performance characteristics that are desired. Flexibility in the design is important to achieving the performance objectives and this does not fit well with the use of mass produced parts. Accordingly, custom designed pumps are not a good fit with investment casting technology.
The internal casing components, such as the volute and diffuser, can be machined from solid metal stock. Such machining can produce precise dimension control and a good surface finish. However, the cross section of the volute is limited to parallel wall design configurations as the machining tools must be inserted and removed from the interior of the casing. There is little flexibility in the shape that can be machined under such restrictions. These restrictions on the shape of the internal chamber of the volute significantly limit the performance and efficiency characteristics of a pump produced with this technology.
Sand castings can also be used to produce pump casings. However, sand casting does not work well for the internal casings of small pumps or turbines, as the surface finish produced is not smooth enough for good efficiency. Without the necessary level of efficiency such small pumps and turbines have a difficult time being a competitive product. In addition, the cores that are used to create the internal voids such as the volute can shift during the molding or pouring process. This results in the void area being both axially and radially displaced from the desired position. Such shifting results in uneven flow entrances and a loss of efficiency for the pump. In addition, the surface finish of such a cast pump casing is not as smooth as desired to obtain the best flow characteristics and efficiency. Some of the above deficiencies can be reduced by grinding or sanding operations on the cast casing provided that the required tools can fit into the areas that need further processing.
The present invention overcomes the deficiencies of the prior art and allows the construction of pumps that maximize the efficiency and performance for the pump and allows for the cost effective production of unique one off design and construction of volute flow passages